The present invention relates to a plasma arc cutting device having means for removing a deposition from a plasma arc nozzle, and to a method for removing the deposition from the nozzle.
A plasma arc cutting device is well known in the art in which a metallic or non-metallic workpiece is locally melted and cut by a heat energy of the plasma arc passing through a plasma arc nozzle. In a conventional plasma arc cutting method, a through hole is formed in a plate like workpiece as a starting hole by the ejection cf the plasma arc on the workpiece, and thereafter, linear cutting starting from the starting hole is carried out by the plasma arc.
As shown in FIG. 1(a) , the plasma arc cutting device is provided with a nozzle 22, through which a main plasma arc 1 is passed. Within the nozzle 22, an electrode 21 is provided for generating the plasma arc 1. Apparently, the workpiece W and the electrode 21 are connected to a power source for generating the main plasma arc 1 between a tip end of the electrode 21 and the surface of the workpiece W. An annular space is provided between the electrode 21 and the nozzle 22.
For forming the starting hole in the workpiece W, material of the workpiece W melted by the plasma arc 1 is splashed as spatters 2 since the melted material cannot be directed to a proper location. Parts of the spatters may be reflected on the surface of the workpiece W, and are directed upwardly to the nozzle 22. The reflected molten material may be deposited on the nozzle 22, and the deposition may be largely grown as shown in FIG. 2(b). If this deposition is grown to a certain mass, another arc 4 between the electrode 1 and the nozzle 22 and arc 5 between the deposition 3 and the workpiece W are generated in addition to the main arc plasma 1. Such plurality of arcs may degrade the workpiece cutting efficiency and may deteriorate the cutting contours in the workpiece.
If the deposition 3 is further grown to reach the workpiece W, the main plasma arc 1 may disappear, and large internal plasma arc 6 may be generated between the electrode 21 and the nozzle 22 as shown in FIG. 1(c) . This internal plasma arc 6 may deteriorate the nozzle 22.
According to the conventional plasma arc cutting device, however, no particular attention is drawn to such a deposition 3 onto the nozzle 22. An operator is, therefore, obliged to manually remove the deposition by using a file, etc. Such manual removal of the deposited material 3 may be troublesome. Particularly, if the plasma arc cutting device is operated under Numerical Control (NC) in which the device is automatically operated, the working efficiency may be extremely lowered if monitoring the state of the deposited material and if intermittently breaking off the cutting operation for conducting the manual operation in order to manually remove the deposited material.